。
Don't come unless I tell you to come.
Literal
Come [quotative-と] say-not [as-long-as-限り] come-not-so-that.
~ない限り is a negative conditional meaning 'as long as X is not / unless X.' 限り ('limit / extent') attached to a negative produces this 'unless' sense. The final ように is a soft negative instruction — 'please don't.' 来なさい is the polite imperative quoted.